Power Performance Test

Table 4 is an equipment list that provides the requirements and specifications for each of the instruments used for performance testing. Figure 4 shows the overall locations of the instrumentation. Figure 5 shows the location of instruments at the top of the meteorological tower.

Figure 5. Detail of instrument locations and mounting booms on the meteo tower.

In addition to the instruments listed in Table 4, the performance test requires a signal to determine turbine operational status.

For the Bergey Excel with Gridtek inverter, the logbook will be checked on manual resets of inverter faults. The logbook will also be checked for further information on turbine availability (DAS or turbine maintenance). If the grid goes down, power to the power transducer is lost and the power signal is invalid; in this way, those data points will be sorted out automatically.

8.2 Test Preparations

In preparation for the test, the test technician will:

• install and check all instrumentation for the power performance test using procedures defined in this section of the test plan

• perform a series of "in-field" checks on each of the instruments

• leave the datalogger in "logging" mode to collect a short, 6-12 hour, data set. This data set will be checked to identify any problems that might not be apparent in the in-field checks.

• perform a third check if a data acquisition system is available that can provide comparable signals to those monitored by the NREL system. In this check, data sets are compared to identify any unexplainable differences in any of the comparable signals.

In parallel with instrumentation checkouts, the turbine owner will:

• complete final modifications to the test turbine and test site, if any

• notify NREL in writing that the turbine and test site configurations are fixed

• provide NREL with updated information on the final test configuration of the turbine and the test site.

After all instrumentation checks are complete, and upon receipt of verification that the turbine and test site configurations are fixed, NREL will change the site identification code on the datalogger to signify the beginning of testing. NREL will also inform the NWTC management that the test has begun.

8.3 Measurement Procedures

Measurements during the power performance test will be obtained automatically by the Campbell datalogger at a sample rate of 1 Hz. At the end of each 10-minute period, as indicated on the datalogger's clock, it records the averages of these data with their standard deviations and minimum and maximum values for the ten minutes. It also records the percentage of time that the turbine or system is not available. Finally, the logger records the number of samples in each record. If the datalogger is interrupted by a program change, its first or last record will contain less than 10 minutes. The IEC standard does not allow use of such records.

On a weekly basis, NREL will transfer data from the datalogger to computers at NREL offices. Also on a weekly basis, NREL personnel will check instruments located on the meteorological tower from ground level. They will note whether there are any obvious failures such as broken or missing cups from the anemometers; bent, broken, or missing wind vane; or misalignment of any sensors. They will also note whether 120 VAC power is being provided to the datalogger. NREL personnel will also record any unusual occurrences with the turbine or instrumentation in the appropriate logbook inside the turbine control shed.

NREL will analyze the data sets once per week. Using the procedures described in the next section, the test engineer will note whether any problems have arisen. The test will be considered as suspended pending resolution of the problem. The test engineer will determine whether data obtained during the period when the problem was active can be used in the determination of power performance and note whether data are used in the test report.

If the test site or turbine changes during the test, the test engineer will determine whether it is appropriate to continue the test, restart the test, or cancel the test. All actions will be documented in the test report. NREL will monitor the quantity of data obtained during testing and will report on test progress to NREL management on a weekly basis.

The power curve must be well defined over a range of wind speeds specified by the IEC standard. In this test, the low end of the range is 2.1 m/s, which is 1 m/s below the Bergey Excel's cut-in wind speed. The high end of the range is 20 m/s, which is 1.5 times the wind speed at which the turbine produces 85% of its rated power. The test will continue until 180 hours of usable data have been obtained in the specified wind speed range and when each 0.5 m/s wind bin in this

range contains at least 30 minutes of data. Once sufficient data are obtained to fulfill these requirements, the NREL test engineer will inform NREL management that the test is complete.